Supernova Remnants Dance in the LMC

January 8, 2008

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Figure 1: Newly released optical image of DEM L316 made with GMOS on Gemini South. This image was obtained as part of the Gemini Legacy Imaging Survey which is led by: P. Michaud, S. Fisher, and R. Carrasco from Gemini and T. Rector from the Univ. of Alaska at Anchorage.

The Gemini South Multi-Object Spectograph (GMOS) recently captured a
dramatic image of a vast cloud complex named DEM L316 located in the
Large Magellanic Cloud. The peanut-shaped nebula appears to be a single
object, but the latest research indicates that it is really comprised of
two distinct gas and dust clouds formed by different types of
supernova explosions.

The new image reveals the intricate tendrils of gas and dust located in
the remnants of the stellar explosions that created the still-expanding
cloud complex. The object was first recognized in the early 1970s as a
supernova remnant, a type of object that is enriched with elements
created in stellar explosions. The nebula was likely created a few tens
of thousands of years ago by more than one type of supernova exploding
in this region of the Large Magellanic Cloud.

S. Points/C. Smith/MCELS/NOAO/AURA/NSF

Figure 2: (background) Wide-field image of DEM L316 and its surroundings in the LMC as seen by the MCELS survey. The inset shows the extent of the new Gemini image.

"The remarkable clarity of these Gemini-South observations shows the complex shock structure of these two supernova remnants in impressive detail," said Dr. Rosa Williams of Columbus State University, an astronomer who has studied DEM L316 extensively. "It's a great step forward in efforts to understand this fascinating pair of remnants - whether they represent only a chance alignment on the sky or some as-yet uncovered physical relationship."

Other recent observations of DEM L316 by the Chandra and XMM-Newton
X-ray space telescopes have strengthened the idea that the cloud is
actually two supernova remnants that are aligned in the sky by chance
and not a single remnant with a distorted bi-polar shape. The Chandra
observations reveal that the chemical compositions of the two shells are
very different. This is a strong hint that they were created in very
different types of supernova outbursts. The data show that the smaller
shell (lower left in the GMOS image) contains significantly more iron
than the larger one. The high abundance of iron in the small bubble
indicates that the gas is the product of a Type Ia supernova. This type
of explosion is triggered by the infall of matter from a star onto a
white dwarf. Since white dwarf stars are extremely old objects, the
system must have been a few billion years old when this supernova
explosion took place.

By contrast, the larger, less iron-rich bubble is the result of a Type
II supernova that was triggered by the collapse of a massive star (more
than seven times the mass of our Sun) when it was only a few million
years old. Since the two progenitor systems had vastly different ages
when they “went supernova”, there is little chance they came from the
same system. Therefore, while the detailed structure seen in the GMOS
image makes it look like the two bubbles are colliding, they only seem
to be close together in the sky because of a chance alignment in our
line of sight.

The Large Magellanic Cloud is a sister satellite galaxy to our Milky Way
and lies about 160,000 light-years away in the direction of the
constellation Dorado. The DEM L316 nebula is located within the LMC and
its two bubbles extend over a distance of about 140 light-years (roughly
35 times larger than the distance between our Sun and its nearest
stellar neighbor).

DEM L316 was also imaged as part of The Magellanic Cloud Emission Line
Survey (MCELS) survey. Wide-field images of the target and its surroundings in the LMC are available here and here.

Rosa Williams of Columbus State University and You-Hua Chu of the University of Illinois published an extensive study of the double supernova remnant in the Astrophysical Journal (ApJ, 635, 1077, 2005). In that paper the authors also review previous work on this target.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, and the Brazilian Ministério da Ciência, Tecnologia e Inovação. The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.